The present invention pertains to systems for underwater geophysical prospecting utilizing a means for producing a sound, or shock wave underwater and a device for detecting and recording the frequency and amplitude of the timed shock impulses as they reflect off of the geophysical structure beneath the sea.
Various devices have been used in an effort to create these micro-second timed sound or shock pulses, including explosives, the bursting of inflatable gas bags, high-voltage sparks and explosive gas mixtures, all posing obvious safety hazards. Pneumatic sound sources providing the timed shock waves are much more efficient in terms of controlling frequency, amplitude and "firing time," not to mention the high factor of safety as compared with previous methods.
Commonly in usage presently are a number of compressed air sound wave pulse generators. These devices generally comprise a piston within a cylinder constructed to release a certain amount of compressed gas in controlled time intervals by reciprocal movement of the piston, cylinder, sleeve or other valving-type mechanism therewith. An inherent shortcoming of compressed gas pulse generators of this reciprocating movement type is the fact that a finite time is required for the reciprocating valve mechanism (piston, sleeve, etc.) to move in one direction to open, to stop and to reverse direction to close. The inherent inertia of metal valving mechanisms simply will not permit this reciprocating motion to occur within a few thousandths of a second.